who caused the death of romeo and juliet???
What a good question! And one to which there is no one simple answer.
First, there is a potentially deadly situation: two powerful families who have been at war for as long as anyone can remember. By falling in love and insisting on being together, the lovers place themselves in grave danger. The fact that their passion is stronger than their sense of risk is another cause: their youthful folly, and the excitement of secret meetings. This is aided and abetted by Juliet's Nurse - who allows sentiment to assist putting her young charge, and her lover, at risk.
Rashness, especially Romeo's suicide when he believes Juliet to be dead and cannot live without her, is yet another factor - had he waited another few moments, he would have discovered she was alive after all. And Friar Lawrence, by suggesting such a drastic ruse, must take his share of the blame too. Whether this play lays blame on youthful impetuousness, or on the follies of those older and wiser who should have known better, is something that has posed questions for audiences ever after.
However, the one single cause of their deaths is their author: Shakespeare himself. The play is a tragedy, and in the Prologue tells us that the 'star-cross'd lovers' will 'take their life' - we can only wait for a tragic, fateful ending. It is as if Love, or this love, so young, so passionate, and so sudden, cannot be sustained and must kill the lovers - and the constant references to love/sex and death occur throughout the play, as do the extremes of love and hate. Yet it is not simple - and the play provides plenty of human agencies of the outcome (including the lovers themselves, who after all do kill themselves) and almost cliff-hanging moments when the audience can see what the protagonists cannot. Shakespeare leaves us with the irony that the Montagues and Capulets call a truce once the lovers are dead.